1. Field of the Invention
The present invention relates to a lens barrel having an image-shake correction optical means arranged, for example, to detect vibrations occurring in the lens barrel as information to be used for preventing image shake and to cause the image shake to be suppressed by moving the image-shake correction optical means in a direction perpendicular to the optical axis of the lens barrel.
2. Description of Related Art
Conventional cameras are arranged to automatically carry out all important actions, such as exposure control and focus auto-control, so that even a person unaccustomed to operating cameras can take pictures with little risk of failure. Further, a system for correcting image shake by detecting vibrations applied to the camera has recently been developed as disclosed, for example, in Japanese Laid-Open Patent Application No. HEI 3-188430.
The frequency of vibrations applied to the camera from the hands holding the camera in taking a picture is normally within a range from 1 Hz to 12 Hz. In order to take a picture without image shake despite occurrence of such vibrations at the time of a shutter release, it is necessary to detect the vibrations of the camera caused by the hands holding the camera and to correct any changes taking place in the direction of an optical axis with a correction optical means according to the amount of the vibrations detected.
The vibration detecting action can be carried out theoretically by providing a camera or a lens unit with a vibration detecting means for detecting an angular acceleration, an angular velocity, an angular displacement, etc., and an image-shake detecting means for electrically or mechanically integrating a signal output from the vibration detecting means and for outputting a signal indicating an angular displacement as detection information. Then, an image-shake suppressing action can be carried out by driving, according to the detection information, a correction optical means which is arranged to decenter a photo-taking optical axis.
FIG. 6 is a perspective view showing an image stabilizing system using the vibration detecting means. Referring to FIG. 6, a vibration detecting means 2 and a correction optical means 3 are disposed between lens units inside a lens barrel 1, so as to constitute the image stabilizing system for suppressing image shake caused by vibrations in the directions of two arrows P and Y, i.e., vertical (pitching) vibrations of the camera and horizontal (yawing) vibrations of the camera.
The vibration detecting means 2 is composed of a detecting means 2p for detecting vertical vibrations of the camera indicated by a line p' and a detecting means 2y for detecting horizontal vibrations of the camera indicated by a line y'. The correction optical means 3 is provided with coils 4p and 4y which are arranged to give thrusts, and detecting elements 5p and 5y which are arranged to detect the positions of the correction optical means 3. The correction optical means 3 is further provided with a position control loop, which is arranged to drive and move the correction optical means 3 by using the output of the vibration detecting means 2 as a target value in such a way as to reliably stabilize an image obtained on the image surface 6a of a film 6.
In the case of a video camera disclosed in Japanese Patent Publication No. HEI 6-28409, the correction optical means 3 which is rotatably supported is arranged to be controlled either in a mode of following up panning or in a mode of not following up panning. The video camera is provided with a change-over switch for selecting the panning follow-up mode or the panning non-follow-up mode. The change-over switch and a recording switch are arranged within one and the same switch means. Further, a photo-taking device disclosed in Japanese Patent Publication No. HIE 6-36571 also has the correction optical means 3 rotatably supported therein. In the photo-taking device, a switch is provided for selection between an image stabilizing photo-taking mode and a panning photo-taking mode. In the panning photo-taking mode, the correction optical means 3 is arranged to have a displacement gain increased to be larger by at least two times the displacement gain in the image stabilizing photo-taking mode.
In each of the conventional examples mentioned above, however, if the image-shake correcting action is arranged to be carried out in an unequivocal and fixed manner, in a case where the lens barrel is intentionally moved by the operator, for example, in performing panning or in following up a finely moving object of shooting, this operation is detected and mistaken for vibrations. In such a case, the lens barrel would come to erroneously carry out a driving action for image-shake correction. As a result, an image as viewed on a viewfinder tends to sway backward in a manner called a "backward shake". With the backward shake having occurred, if the operator attempts to move the lens barrel to correct it, such an attempt would bring about another backward shake, which makes it extremely difficult to follow up the object. Further, while an automatic focusing action on the lens is in process, such a backward shake frequently brings the object out of a focusing frame, thereby bringing the lens barrel into a defocusing state. Then, a shutter operating opportunity tends to be missed under such a condition.
To solve the above-stated problem, in the video camera disclosed in Japanese Patent Publication No. HEI 6-28409, the recording switch is arranged to serve also as a change-over switch for selection between the panning follow-up mode and the panning non-follow-up mode. In carrying out the control mode change-over, however, the recording switch might be completely turned off by mistake. Further, the image stabilizing characteristic of the video camera is hardly satisfactory for a normal shooting operation in the non-follow-up mode. Therefore, the quality of images obtained by shooting after panning becomes inadequate. The same problems exist also in the photo-taking device disclosed in Japanese Patent Publication No. HEI 6-36571 mentioned above.
Further, in a case where the lens barrel having the image-shake correction optical means is secured to a tripod, the operation of the shutter might cause vibrations of high frequency in the direction of pitching. The frequency component of the ordinary driving signal for image-shake correction differs too much from the high frequency of the vibrations to adequately correct the image shakes. To solve this problem, therefore, a switch for the image-shake correction must be turned off for a shooting operation in that case.